1. Field of the Invention
The invention relates to operation of an internal combustion engine as a function of engine operating parameters.
2. Prior Art
Not every combustion process, including that which takes place within an internal combustion engine, goes to completion. One product of incomplete combustion is carbon monoxide. Carbon monoxide, when inhaled in sufficient quantities, can have undesirable effects on the human body. Even though emission control devices have been installed in U.S. automobiles since 1975, idle operation in an enclosed space can cause a condition which results in elevated concentrations of carbon monoxide in the air of the enclosed space. The present invention is aimed at preventing elevated concentrations of exhaust gases in the ambient.
U.S. Pat. No. 4,221,206 teaches the use of two carbon monoxide (CO) detectors, one electrical and the other electromechanical, and deactivating a vehicle engine only when the signals from both CO detectors indicate the presence of CO above a predetermined amount. Such a system may cause undesirable interruption of engine operation when the vehicle is moving as a result of temporarily high CO concentrations originating from passing nearby exhaust gas sources such as heavy-duty vehicles, tractors, or earth moving machinery. It would be desirable to obviate sudden disablement of a moving vehicle triggered by an extraneous event such as being near an exhaust pipe of a heavy-duty vehicle or any other chance source emitting a relatively high concentration of carbon monoxide in the exhaust gas.
FIG. 3 shows, schematically, the time evolution, after initiation of vehicle idling operation in an enclosed space (e.g., a garage), of: (a) the A/F ratio of the engine; (b) the width of the fuel pulse injected sequentially to each engine cylinder; (c) the time averaged HEGO (heated exhaust gas oxygen) or EGO (exhaust gas oxygen) sensor signal; (d) the oxygen concentration in the enclosed space; and (e) the rate of emitted CO as well as the resulting concentration of CO in the enclosed space. After a few seconds following ignition, the A/F ratio is maintained at the stoichiometric value by the feedback controlled fuel metering system. Under this condition, and for a properly functioning three-way catalyst, the production rate of CO is very small (and constant) and its concentration in the enclosed space rises only very slowly.
As time passes, oxygen is depleted from the air in the enclosed space. Consequently, less fuel is required to keep the A/F ratio at stoichiometry, and the width of the fuel pulse will continuously be decreased by the control system. After a certain time T.sub.1 has elapsed, the width of the fuel pulse reaches the minimum value specified by the design of the fuel metering system. At that point, the A/F ratio begins to drift into the rich region and the HEGO sensor signal increases to a high value as seen from the HEGO sensor signal versus air/fuel ratio (A/F) relationship shown in FIG. 4. At the same time, the rate of tail pipe CO production rapidly increases for two reasons: first, the concentration of CO in the gas emerging from the engine increases, and, secondly, the efficiency of the three-way catalyst for CO oxidation rapidly decreases to zero as the A/F becomes richer and richer. The engine will continue idling until, at time T.sub.2, the A/F becomes so rich (e.g., A/F=6) that combustion cannot be maintained. Even though engine operation terminates at this time, the carbon monoxide level may already have reached a dangerous level for occupants in the vehicle passenger compartment. It would be desirable to have a system which would avoid such a carbon monoxide buildup.